Speed control device

ABSTRACT

A grinding machine has a grinding wheel advancing mechanism having at least two speeds of operation, and a hydrostatic spindle for supporting a workpiece. Detector means are provided for detecting the change in pressure of the support fluid of the hydrostatic spindle when the grinding wheel contacts the workpiece supported on the spindle. Speed changing means are provided, responsive to the output of the detector means, for effecting a change in the speed of the advancing mechanism of the grinding wheel.

United States Patent Pesante 51 June 27, 1972 54 SPEED CONTROL DEVICE 2,961,808 11/1960 Dunigan ..Sl/165.92 2,984,952 5/1961 Gebel ..51/l65.9 [72] lnventor: Manllo Pesante, Turin, Italy [73] Assignee: RIV-SKF Officlne d1 Villar Perosa S.p.A., Primary g Turin Italy Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [22] Filed: Feb. 27, 1970 [21] Appl. No.: 14,907

ABSTRACT Apllucluoll Data A grinding machine has a grinding wheel advancing March 4 [969 my "50838Al69 mechanism having at least two npcodl of operation. and a hydrostatic lplndle for suppnrtlng l workplace. Detector 52 us. Cl ..s|/|6s.17 means 11mmd [51] lnt.Cl ..B24b49/08 support fluid 0f the hydrostatic spindle when Srindinfl 5s Fleld 61 Search ..51/l65.74, 165.75, 165.76, wheel contacts the workpiece supported on the spindle Speed 5 5 77 1553 |55 9 1 532 1 3 changing means are provided, responsive to the output of the detector means, for effecting a change in the speed of the ad- [56] References Cited vancing mechanism of the grinding wheel.

UNITED STATES PATENTS 10 Claims, 1 Drawing Flgure 2,639,562 5/1953 Balsiger ..51/165.75 X 2,802,312 8/1957 Gosney et a1. .......$1/l65.92

' Mama/14E r5 TWO SPEfD GRIND/N6 PATENTEDJUHZY I972 1672.100

11 TP/06f/Q l J 1O POWER AMPL M755 2 1% mm me SPEED CONTROL DEVICE The present invention relates to a speed control device. This device is particularly useful for a grinding wheel advancing mechanism in a grinding machine of the kind in which a workpiece is supported by a hydrostatic spindle.

in grinding operations, and particularly for work produced in large series it is necessary to reduce to a minimum the time lost in the so-called mid-air" phase, that is, when the wheel is not in contact with the workpiece. It is desirable to achieve the highest possible speed of approach of the grinding wheel to the workpiece, and then to change to a slower speed of advance when the wheel has come into contact with the workpiece.

According to one aspect of the present invention a speed control device for a grinding wheel advancing mechanism having at least two speeds of operation in a grinding machine of the type having a hydrostatic spindle for supporting a workpiece comprises detector means responsive to pressure variations in the supporting fluid of the hydrostatic spindle, and means responsive to the output of the detector means for changing the speed of operation of the advancing mechanism. Preferably the two speeds of operation of the advancing mechanism are an approaching speed and a working speed, and the detector means are responsive to the pressure variations in the support fluid as the grinding wheel contacts the workpiece at the approach speed for changing over to the working speed.

The changeover from the speed of approach to the working speed preferably occurs at the moment at which the wheeljust touches the workpiece in order to reduce to a minimum the period during which the wheel is inoperative.

According to another aspect of the invention a speed control device for controlling the speed of advance of a grinding wheel in a grinding machine having a hydrostatic spindle for carrying a workpiece employs the operational steps of detecting the variations 'of pressure in the support fluid of the hydrostatic spindle when the grinding wheel is brought into contact with a workpiece at an approach speed, and effecting a change from the approach speed to a working speed in response to said detected pressure variation. The changeover of speeds has to occur substantially instantaneously with the moment of contact between the wheel and the workpiece so as not to cause grinding burns on the work and not to warp it.

Preferably the detector means includes a differential manometer which may have an electrical output or alternatively may have an hydraulic or a pneumatic output. Preferably the means responsive to the output of the detector means includes a trigger which initiates the speed change in response to a threshold output from the detector means.

It is inconvenient to introduce additional members, such as dynamometers which, apart from the amount of space required for installation, would upset the static and dynamic rigidity between the grinding wheel and the workpiece, with consequent generation of vibrations harmful to the grinding operation.

One embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing which is a part schematic block diagram of the embodiment.

Referring now to the drawing, reference 1 is a grinding wheel which is mounted on an advancing mechanism shown schematically at 14.

A hydrostatic spindle generally indicated at 2 is shown supporting a workpiece 3.

The spindle 2 has its axis parallel to that of the wheel 1 and is so positioned in relation to the wheel 1 that the advancing movement of the wheel 1 is along a line joining the axes of the wheel I and the spindle 2.

The spindle 2 consists of a cylindrical support shaft 4 upon which there is slidingly assembled a hydrostatic cushion 5 supported by supporting fluid and supporting in its turn the workpiece 3.

In order to achieve the hydrostatic support of the cushion 5, it is formed upon its inner side, that is, the surface facing the shaft 4, with a number of chambers 6, distributed upon the said surface facing the shafi, and into which fluid under pressure can flow.

There are four such chambers in the embodiment shown but there may be more providing there are an even number so as to provide symmetrical support.

To two of the chambers 6, which are in the line joining the axes of the spindle 2 and the wheel 1, and marked 64 and 66 respectively, there are connected two tubes, marked 7 and 8 respectively, which lead to respective input sides of a differential manometer 9.

The differential manometer 9 transduces any differences of pressure in the fluid in the tubes 7 and 8 into an electrical output signal, the amplitude of which is proportional to the difference in pressure of the fluid in the tubes 7 and 8.

Electronic devices for transducing pressure differences into electric signals are many; for example, among the most commonly used are electrical transducers called strain gauges" and pick-ups, with inductive and capacitative proximity, with a differential transformer.

The electrical output signal of the differential manometer 9 passes to an amplifier l0, and thence to an electronic trigger II with an adjustable threshold.

The trigger ll triggers a power amplifier 12 which feeds an activator 13 which drives the parts of the advancing mechanism 14 to control the speed of advance of the wheel I.

The device works in the following manner:

The wheel 1 is advanced toward the workpiece 3 at the relatively higher approach speed.

When the wheel I touches the workpiece 3, there is a rise of pressure in the fluid contained in the chamber 61:, and a decrease of pressure in the fluid contained in the chamber 60.

These variations in pressure are propagated in the form of pressure waves along the tubes 7 and 8 and are registered by the differential manometer 9.

Transmission of the variation of pressure in the chambers 60 and 6b to the manometer 9 is substantially instantaneous, inasmuch as, depending on the nature and the pressure of the fluid used for hydrostatic support of the cushion 5, the pressure waves, which are propagated to the tubes 7 and 8 travel at the speed of sound in the fluid, of the order of 1.2 km. per second. The differential manometer 9 has a sensitivity of the order of l/5,000 of an atmosphere.

The output of the difierential manometer 9 is, as has already been said, an electrical signal of amplitude proportional to the value of the differential pressure, which is amplified by the amplifier 10. The amplified signal acts on the trigger" ll which has an adjustable threshold. This makes it possible to determine the level of pressure above which the speed changeover must occur.

The output signal of the trigger" 11 is amplified by the power amplifier l2 and then passes to an activator 13. The power amplifier I2 is necessary because the activator I3 is the active element of the circuit. In other words the activator [3 acts upon the drive 14 of the grinding wheel advancing mechanism to reduce its speed to that determined for the particular grinding operation desired.

The said activator 13 may be a hydraulic or pneumatic pilot valve, or a motor circuit switch, or an electrolytic valve, according to the means used for the grinding wheel advancing mechanism.

In an alternative embodiment of the invention, where the differential manometer is of the fluid or pneumatic type, the output signal of the manometer is of the fluid pressure type. This fluid signal can be converted into an electric signal before being amplified, or can be used to feed the pilot circuit of an electrolytic valve so as to give, as an output, a fluid signal proportional to that of the input.

In this latter case the successive blocks in the drawing (ll, l2, l3, 14) to the amplifier [0, are of the fluid or pneumatic type.

I claim:

l. in a grinding machine having a grinding wheel, an advancing mechanism for said grinding wheel, said advancing mechanism having at least two speeds of operation, a hydrostatic spindle for supporting a workpiece, and support fluid in said hydrostatic spindle, the improvement comprising detector means responsive to pressure variations in said support fluid, and speed control means responsive to the output of said detector means to change the speed of operation of said advancing mechanism.

2. The grinding machine of claim 1 wherein said advancing mechanism has an approach speed and a working speed, said detector means produces said output when the pressure in said support fluid changes as said grinding wheel contacts said workpiece at said approach speed, and said speed control means changes the speed of said advancing mechanism from said approach speed to said working speed.

3. The grinding machine of claim 1 wherein said detector means includes a differential manometer, two chambers in said hydrostatic spindle for containing support fluid, and connecting means interconnecting said two chambers and respective input sides of said differential manometer,

4. The grinding machine of claim 3 wherein said two chambers in said hydrostatic spindle are diametrically opposed across said spindle and in a line joining the axes of said grinding wheel and said hydrostatic spindle.

S. The grinding machine of claim 3 wherein said differential manometer has an electrical output.

6. The grinding machine of claim 3 wherein said differential manometer has a pneumatic output.

7. The grinding machine of claim 3 wherein said differential manometer has an hydraulic output.

8. The grinding machine of claim 1 wherein said speed control means responsive to the output of said detector means includes trigger means, said trigger means initiating said change in speed of said advancing mechanism in response to a threshold output from said detector means.

9. The grinding machine of claim 8 wherein said trigger means is adjustable to vary the threshold output from said detector means required to tire said trigger means.

10. In a grinding machine having a grinding wheel, an advancing mechanism for said grinding wheel, said advancing mechanism having at least two speeds of operation, a hydrostatic spindle for supporting a workpiece, and support fluid for said hydrostatic spindle, the improvement comprising:

detector means responsive to pressure variations in said support fluid, said detector means including a differential manometer having an electrical output,

first amplifier means for amplifying the output of said differential manometer,

electrical trigger means responsive to a threshold output of said first amplifier means,

second amplifier means for amplifying the output of said trigger means, and

means responsive to the output of said second amplifier means for changing the speed of said advancing mechanism whereby a change in pressure in said support fluid when said grinding wheel contacts said workpiece causes a change in speed of said advancing mechanism. 

1. In a grinding machine having a grinding wheel, an advancing mechanism for said grinding wheel, said advancing mechanism having at least two speeds of operation, a hydrostatic spindle for supporting a workpiece, and support fluid in said hydrostatic spindle, the improvement comprising detector means responsive to pressure variations in said support fluid, and speed control means responsive to the output of said detector means to change the speed of operation of said advancing mechanism.
 2. The grinding machine of claim 1 wherein said advancing mechanism has an approach speed and a working speed, said detector means produces said output when the pressure in said support fluid changes as said grinding wheel contacts said workpiece at said approach speed, and said speed control means changes the speed of said advancing mechanism from said approach speed to said working speed.
 3. The grinding machine of claim 1 wherein said detector means includes a differential manometer, two chambers in said hydrostatic spindle for containing support fluid, and connecting means interconnecting said two chambers and respective input sides of said differential manometer.
 4. The grinding machine of claim 3 wherein said two chambers in said hydrostatic spindle are diametrically opposed across said spindle and in a line joining the axes of said grinding wheel and said hydrostatic spindle.
 5. The grinding machine of claim 3 wherein said differential manometer has an electrical output.
 6. The grinding machine of claim 3 wherein said differential manometer has a pneumatic output.
 7. The grinding machine of claim 3 wherein said differential manometer has an hydraulic output.
 8. The grinding machine of claim 1 wherein said speed control means responsive to the output of said detector means includes trigger means, said trigger means initiating said change in speed of said advancing mechanism in response to a threshold output from said detector means.
 9. The grinding machine of claim 8 wherein said trigger means is adjustable to vary the threshold output from said detector means required to fire said trigger means.
 10. In a grinding machine having a grinding wheel, an advancing mechanism for said grinding wheel, said advancing mechanism having at least two speeds of operation, a hydrostatic spindle for supporting a workpiece, and support fluid for said hydrostatic spindle, the improvement comprising: detector means responsive to pressure variations in said support fluid, said detector means including a differential manometer having an electrical output, first amplifier means for amplifying the output of said differential manometer, electrical trigger means responsive to a threshold output of said first amplifier means, second amplifier means for amplifying the output of said trigger means, and means responsive to the output of said second amplifier means for changing the speed of said advancing mechanism whereby a change in pressure in said support fluid when said grinding wheel contacts said workpiece causes a change in speed of said advancing mechanism. 